Mutation of the mouse nodal gene, a member of the TGF-beta superfamily, causes embryonic arrest prior to mesoderm formation. To further characterize the gene we have carried out a range of expression studies: (1) We have examined the effects of ectopic RNA expression on zebrafish development. (2) We have generated functional nodal protein by expression in cultured CHO cells. (3) We have isolated a nodal homologue from the chicken and determined its pattern of expression. The results support a role for nodal in mesoderm formation during the development of many species.